The butterfly valve, as a part used to realize the connecting or disconnecting of the pipeline system and control the flow, has been widely applied in petroleum, chemical industry, metallurgy, water and electricity and many other areas. As the present butterfly valve technology known to the public, it always adopts soft sealing structure as its sealing means, and the sealing materials are rubber, polytetrafluoroethylene etc. Because of the restriction of the structure characteristic, it can't be applied in high temperature, high pressure and corrosion resistance, abrasion resistance, and other industries.
More advanced butterfly valve is tri-eccentricity metal hard sealing butterfly valve, the valve body and valve seat are connecting components, high temperature resistance, corrosion resistance materials are welded on the sealing surface of the valve seat. Multilayer soft and hard overlap sealing ring is fixed on the valve disc. Compared with the traditional butterfly valve, it has the advantage of high temperature resistance, easy operation, no friction in the course of opening and closing. When closing, the torque of gearing increases, to compensate the sealing, thus improves the sealing performance and extends the working life.

But there are still some problems in using this kind of butterfly valve, as following:
1.Because Multilayer soft and hard overlap sealing ring is fixed on the valve disc, the medium frontally flushes the sealing surface when the valve disc keeps opening, if the soft sealing ring in the sheet metal interlayer been flushed, it will directly affect the sealing performance.

2.This structure can not be applied to the valve DN200 during to the resistance of the structure condition, the reason is that the whole structure of the valve disc is too thick, flow drag index it too large.

3. According to the principle of the Tri-eccentricity structure, the sealing between the sealing surface of valve disc and seat is relying on the torque of the gearing device to make the valve disc pressing onto the valve seat. In the condition of obverse flow, the higher the pressure of medium is, the sealing presses more tightly. When the medium flows reverse, as the pressure of medium increases, when the unit pressure between the valve disc and seat is smaller than the pressure of medium, the sealing starts to leak.

Characteristics of the High-performance Tri-eccentricity Double-direction Hard Sealing Butterfly valve are as following:
This sealing ring is composed of soft T-shaped sealing circle made of multiplayer stainless steel sheet .The sealing surface of the valve disc and seat is elliptical structure, high temperature resistance、 corrosion resistance alloy materials are welded on the elliptical surface of the valve seat; and the spring fixed between regulating ring clamping board and the regulating bolts are component of one structure. This structure effectively compensate for the　tolerance margin between the axis guide and the valve body, and also for the elastic deformation under the medium pressure, in the meantime, solve the sealing problem in the Bi-directional interchangeable medium transmission cause. The sealing ring made of soft T-shaped sealing circle of multiplayer stainless steel sheet has double advantage of metal hard sealing and soft sealing. No matter under the condition of low temperature or high temperature both can show the zero-leakage sealing performance.

The experiment shows that in the condition of obverse flow，（the direction of the medium flow is the same with the direction of the disc revolving）, the pressure of sealing surface is caused by the torque of the gearing device and the pressure of the medium acting to the valve disc. When the pressure of the obverse medium increases, the elliptical surface will be more tightened with the sealing surface of the valve seat, and the sealing effect will be much better. In the condition of reverse flow, the sealing between the valve disc and seat is droved by the torque of the driving-device making the valve disc pressed on to the valve seat. As the pressure of reversing medium increases, when the unit obverse pressure between the valve disc and seat is smaller than the pressure of the medium, after the spring of the regulating ring bears carrying，it can save the deformation energy, and automatically compensate for the tighten pressure between the sealing surface of the valve disc and seat

This new-style does not fix soft hard multilayer sealing ring like some other present technology, but directly fix on the valve body, adding the regulating ring between the clamping board and the valve seat is an extremely ideal Bi-directional hard sealing method.